ALBERT

Beschreibung: Greenhouse gas emissions from farms can be suppressed in two ways: by curtailing the release of these gases (especially N2O and CH4), and by storing more carbon in soils, thereby removing atmospheric CO2. But most practices have multiple interactive effects on emissions throughout a farm. We describe an approach for identifying practices that best reduce net, whole-farm emissions. We propose to develop a “Virtual Farm”, a series of interconnected algorithms that predict net emissions from flows of carbon, nitrogen, and energy. The Virtual Farm would consist of three elements: descriptors, which characterize the farm; algorithms, which calculate emissions from components of the farm; and an integrator, which links the algorithms to each other and the descriptors, generating whole-farm estimates. Ideally, the Virtual Farm will be: boundary-explicit, with single farms as the fundamental unit; adaptable to diverse farm types; modular in design; simple and transparent; dependent on minimal, attainable inputs; internally consistent; compatible with models developed elsewhere; and dynamic (“seeing”into the past and the future). The Virtual Farm would be constructed via two parallel streams - measurement and modeling - conducted iteratively. The understanding built into the Virtual Farm may eventually be applied to issues beyond greenhouse gas mitigation. Key words: CO2, N2O, CH4, agroecosystems, models, climate change

Beschreibung: Forest managers are faced with complicated road construction and deactivation decisions. When construction, upgrading, and deactivation strategies must be determined simultaneously over broad spatial and temporal scales, the problem becomes very complex and decision support systems are needed. In this paper, we report the development and application of an optimal road class and deactivation model using dynamic programming. We tested our model on projected road networks on Hardwicke Island, British Columbia. Sensitivity of inputs such as construction costs, upgrade costs, hauling and maintenance costs, deactivation costs, length of time horizon, discount rate, and haul volume were tested within and between two road networks. Comparison of road networks revealed that haul volume concentration, average haul distance, and total road length are the most important variables that affect road class decisions and total network costs. Within our case study, the road network with the lowest average hauling distance resulted in the lowest total cost (CAN$0.24/m3 less), because hauling costs are the largest component (46%) of total transportation costs. The dynamic programming model can be used to assess numerous road construction and maintenance assumptions under various silviculture and harvest systems.

Beschreibung: We examined fifth-year seedling response to soil disturbance and vegetation control at 42 experimental locations representing 25 replicated studies within the North American Long-Term Soil Productivity (LTSP) program. These studies share a common experimental design while encompassing a wide range of climate, site conditions, and forest types. Whole-tree harvest had limited effects on planted seedling performance compared with the effects of stem-only harvest (the control); slight increases in survival were usually offset by decreases in growth. Forest-floor removal improved seedling survival and increased growth in Mediterranean climates, but reduced growth on productive, nutrient-limited, warmhumid sites. Soil compaction with intact forest floors usually benefited conifer survival and growth, regardless of climate or species. Compaction combined with forest-floor removal generally increased survival, had limited effects on individual tree growth, and increased stand growth in Mediterranean climates. Vegetation control benefited seedling growth in all treatments, particularly on more productive sites, but did not affect survival or alter the relative impact of organic matter removal and compaction on growth. Organic matter removal increased aspen coppice densities and, as with compaction, reduced aspen growth.

Beschreibung: The impact of forest management operations on soil physical properties is important to understand, since management can significantly change site productivity by altering root growth potential, water infiltration and soil erosion, and water and nutrient availability. We studied soil bulk density and strength changes as indicators of soil compaction before harvesting and 1 and 5 years after harvest and site treatment on 12 of the North American Long-Term Soil Productivity sites. Severe soil compaction treatments approached root-limiting bulk densities for each soil texture, while moderate compaction levels were between severe and preharvest values. Immediately after harvesting, soil bulk density on the severely compacted plots ranged from 1% less than to 58% higher than preharvest levels across all sites. Soil compaction increases were noticeable to a depth of 30 cm. After 5 years, bulk density recovery on coarse-textured soils was evident in the surface (010 cm) soil, but recovery was less in the subsoil (1030 cm depth); fine-textured soils exhibited little recovery. When measured as a percentage, initial bulk density increases were greater on fine-textured soils than on coarser-textured soils and were mainly due to higher initial bulk density values in coarse-textured soils. Development of soil monitoring methods applicable to all soil types may not be appropriate, and more site-specific techniques may be needed for soil monitoring after disturbance.

Beschreibung: Fast-growing hybrid poplars are being planted in the Canadian prairies to meet the increasing demand for fibre and environmental services of trees and forests; however, the impact of hybrid poplars on C dynamics and storage on previously farmed land is largely unknown for the boreal region. We measured soil CO2 efflux along a chronosequence (3-, 9-, and 11-yr-old stands) of hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantations and a control agricultural field from June to August 2004. Measurements were made between 0800 and 1800 with a portable Li-Cor 6400-09 system and were based on 4–5 min averaging. We also measured the response to simulated rainfall and the diurnal fluctuation of soil CO2 efflux. Soil CO2 efflux ranged from 1.30 µmol CO2 m-2 s-1 in the 3-yr old plantation to 5.41 µmol CO2 m-2 s-1 in the agricultural control field, or from 0.17 ìmol CO2 m-2 s-1 kg-1 C (based on soil organic C content to a 0.4 m depth) in the 3-yr-old plantation to 1.09 µmol CO2 m-2 s-1 kg-1 C in the 11-yr-old plantation. Simulated rainfall applied in the 3-yr-old plantation and a newly planted site resulted in an immediate pulse of CO2 efflux, 2.90 and 2.54 µmol CO2 m-2 s-1, respectively, followed by an efflux rate sustained slightly above pre-irrigation levels. No secondary pulse of soil respiration was observed in the 2-h period following water application. Diurnal variation of soil respiration was found to be small between 0600 and 1900 in the agricultural control field, with values that varied from 2.66 to 3.17 µmol CO2 m-2 s-1. Continued monitoring of soil respiration and other C cycling processes in the chronosequence will improve our understanding of the potential for C sequestration in hybrid poplar plantations in northern Alberta. Key words: Carbon sequestration, greenhouse gas emissions, biomass, boreal forest, land-use change, hybrid poplar

Beschreibung: We investigated plant community responses (abundance, species diversity, and structural diversity) to a range of precommercial thinning densities in young lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands 12 to 14 years after thinning, with both unthinned and old-growth stands for comparison. Abundance of understory plants, especially herbs, appeared to increase dramatically in the thinned stands. The moss layer was significantly more abundant in old-growth stands than in the young pine stands. Of a total of 108 species sampled, only three were introduced species, all of which occurred more frequently in the low-density stands than in any of the other stands. Thinning treatments appeared to increase the abundance of late-seral species. Our results suggest that by disrupting canopy closure, thinning decreased the dominance of tall trees and increased the abundance of herbs, shrubs, and trees in the understory height classes. As a result, thinning to low densities significantly increased the structural richness of the tree layer and caused an increase in total structural diversity, which, although only marginally significant (p = 0.06), was likely biologically important. Our results suggest that thinning will enhance the abundance, species diversity, and structural diversity of the plant community 12 to 14 years postthinning.

Beschreibung: Increasing concern for the amount of P entering lakes in Manitoba may lead to regulation of P concentration in agricultural soils. A possible means for this regulation is the use of soil test P. This may require a means of comparing soil test P analyses as various laboratories in Manitoba employ different methods of soil test P determination. Thus, the objectives of this study were to (i) compare the methods of P determination in Manitoba soils, and (ii) develop equations for converting different soil test P methods from one to another. One hundred and fifteen archived surface soil samples representing major soils of Manitoba were used for the study. Soil test P was determined in these soils using the original Kelowna (K1) method and the two modified Kelowna methods (K2 and K3). Mehlich-3, Olsen- and water extractable-P were also determined for all soils. The results were analyzed statistically and were related using a simple regression analysis model. The amount of P extracted by the different extracting agents varied widely. Mehlich-3 extracted the largest amount of P (a range of 5.4–200 mg kg-1) while water extracted the smallest amount (a range of 0.2–70 mg kg-1). The P extracted by the Olsen and the three Kelowna methods were intermediate between Mehlich-3 and water-P. Our results also showed that the three Kelowna methods were not significantly different from one another. The Olsen method compared well with those of the modified Kelowna methods, but extracted less P than the original Kelowna and Mehlich-3 methods. Overall, the different agronomic soil test P methods were well correlated to each other with correlation coefficients (r) ranging between 0.95 and 0.98. However, the correlations between these soil test methods and water extractable P was not as high. Water extractable P and the agronomic soil test P methods were better related by a non-linear relationship than by a linear relationship. The coefficient of determination (R2) for all the regression equations relating the different agronomic soil test P methods ranged from 0.91 to 0.97. As such, the equations generated in this study can be used to convert the result from one soil test P method to another. Key words: Kelowna extractable phosphorus, Mehlich-3 extractable phosphorus, Olsen extractable phosphorus, water extractable phosphorus

Beschreibung: An unbuffered BaCl2 extraction for determining effective cation exchange capacity (ECEC) and exchangeable cations is often used for acidic forest soils. However, the contribution of exchangeable H+ to ECEC cannot be assessed using this method as H+ in the extract may be produced/consumed in reactions with free Al3+ and Al-OH complexes, or H+ may be added to the extract via non-exchangeable sources. Fundamentally, any valid measure of ECEC must include some estimate of exchangeable H+ concentration or a demonstration that it is negligible. Unfortunately, this procedure is often neglected in forest soil studies. In this paper, we assessed the significance of the contribution of exchangeable H+ to ECEC for upper soil horizons of three sites of Quebec’s Boreal Shield subject to various disturbance types (i.e., recent harvest, fire and mature forest). We also investigated whether the linear relationships between exchangeable H+ concentrations and soil pH are robust enough to develop regression models capable of predicting exchangeable H+. Exchangeable H+ in the FH samples was higher than that in the podzolic B samples, but the amount of adsorbed H+ relative to ECEC was nevertheless significant in the podzolic B horizons. The general linear relationship (i.e., FH and podzolic B samples as a single data set) developed from soil pH in water explained close to 70% of the variability of log (H+/ECEC). The relationships between log (exchangeable H+) and pH in water in the FH samples were however superior (R2 ≥ 80), either for all sites, disturbance types and sampling strategies (e.g., proportions of F and H horizons in sample). The relationships developed for podzolic B samples alone were not as strong, but ECEC was used efficiently in combination with soil pH to increase prediction capabili ties (R2 ≥ 0.61). Key words: Boreal Shield forest soils, effective cation exchange capacity, exchangeable H+, fire, FH and podzolic B horizons, harvesting, prediction models, soil pH.